1. Field of the Invention
This invention relates to a process for manufacturing a lead frame which includes the electrolytic polishing of a blank for a lead frame as a pretreatment prior to plating, and more particularly, to an improvement in the method for the electrolytic polishing of a blank for a lead frame which employs a contactless electrolytic polishing apparatus.
2. Description of the Prior Arts
The Prior Art
A lead frame as a material for an electronic part is usually manufactured by punching a rolled material, such as copper or steel, to prepare a blank for a lead frame, polishing the blank electrolytically to give it a smooth surface and remove oil and fat, etc., from any protruding and recessed portion thereof, removing any oxide film from the electrolytically polished surface of the blank, and plating it with a metal such as copper, silver or palladium.
The smoothness of the polished blank has a critical effect on its metal plating, and particularly when a palladium-plated lead frame is manufactured, it has been necessary to employ a complicated process which includes plating the electrolytically polished blank with a strike of nickel after removing any oxide film therefrom, forming an electroplated layer of nickel having a thickness of 1 to 2 microns thereon, and plating it with palladium.
Moreover, the conventional electrolytic polishing process has been incomplete in the removal of any protrusion and concavity from the surface of the blank, and therefore, its subsequent plating with a strike of copper or nickel provides a lead frame which is defective due to the protuberances on or unevenness of its plated surface, thereby presenting an obstacle to a reduction of cost.
Therefore, if it is possible to decrease any protrusion and concavity from the surface of the blank for a lead frame, it is possible not only to overcome those problems, but also to plate the electrolytically polished blank with a metal directly or after coating it with an inexpensive strike of copper, and thereby achieve a drastic reduction of cost, depending on the material of the blank. Accordingly, various attempts have been made to obtain an improved method for electrolytic polishing.
A method employing a contactless electrolytic polishing apparatus has been proposed as one of the electrolytic polishing methods which have hitherto been under consideration. This method employing a contactless electrolytic polishing apparatus enables the electrolytic polishing of the blank without causing its deformation, since its polishing can be done without its contact with the electrode, but the mere passing of a direct current between the two poles for the electrolytic polishing of the blank has been unable to give it a satisfactory smoothness, and moreover, the short life of the electrode has made it impossible to continue any electrolytic polishing operation for a long period of time.